Ecdysone and 20-hydroxyecdysone have been implicated as possible hormonal regulators of several posteclosion gonadotropic maturation events in adult female Aedes mosquitoes. However, because of a paucity of basic information about ecdysteroids (e.g., biosynthesis, hemolymph titer, regulation of biosynthesis and titers) during the gonadotropic cycle of Aedes, the physiological role(s) of ecdysone and 20-hydroxyecdysone in Aedes reproduction remain(s) conjectural. The primary objective of the proposed research is to elucidate the physiological/endocrinological mechanisms regulating the titers and biosynthesis of ecdysteroids in adult female Aedes aegypti and Aedes atropalpus. These studies will entail: 1) measurements of the whole body, hemolymph and ovarian ecdysteroid titers during the gonadotropic cycle; 2) characterization and quantification during the gonadotropic cycle of ecdysone 20-monooxygenase activity, the enzyme system which is responsible for the conversion of ecdysone to 20-hydroxyecdysone; 3) identification and critical period determination of the factors (endocrine and dietary) which may be responsible for the activation/regulation of ecdysone 20-monooxygenase activity; and 4) in vivo perturbations of ecdysone 20-monooxygenase activity to assess its relative significance, as well as that of 20-hydroxyecdysone, during the gonadotropic cycle. Methodologies incorporated into the proposed research include: radioimmunoassays, monooxygenase radioassays, organ culture, polyacrylamide gel electrophoresis, radio-immunoprecipitation assays, classical endocrinological techniques, and ecdysteroid/cytochrome P-450 biochemical and chemical techniques. It is anticipated that the studies proposed will lead to a much more detailed and clearer understanding of the endocrine axes operating during the gonadotropic cycle of Aedes (particularly with respect to ecdysteroids) and that such information may eventually be useful in the development of new ways to disrupt reproduction in medically important vector mosquitoes.